Color analysis

ABSTRACT

Techniques related to printing are described herein. According to an example, color patches are to be printed on a substrate. The substrate can be positioned on a substrate support for operation of a color sensor in a color measurement zone. Dimension and location in the substrate of the color patches are selected such that, for each color patch, at least a portion of the color patch can be positioned on a support projection in the color measurement zone. In some examples, color analysis techniques are described.

BACKGROUND

The colors produced by color printers can vary as a function of mediatype, ink, print heads, temperature, humidity, etc. To address colorvariation, color characterization instruments (e.g., spectrophotometers)and device characterization profiling tools (e.g. International ColorConsortium (ICC) profiles) for devices such as printers may be created.Device characterization profiling facilitates proper color handling.

In order to create a printer color profile, a printing system may printa test color pattern. For example, a test color pattern may be printedincluding a plurality of color patches arranged in a predeterminedpattern. A color measurement device (e.g., a spectrophotometer or acolorimeter) may scan the test color pattern, and the color measurementsmay be used to create a profile for the printer that can be used toinsure printing colors in a consistent manner.

There are a variety of methods for analyzing colors printed on asubstrate. Such methods include, for example, using a hand-heldspectrophotometer including a wheel that contacts the color patches onthe paper. The wheel is for maintaining a desired spatial relationshipbetween the spectrophotometer and the paper. As the spectrophotometer ismoved, the wheel measures the speed and direction of the movement whilethe spectrophotometer determines color on locations across thesubstrate.

In some other methods, a color sensor (e.g., a spectrophotometer or acolorimeter) is mounted in the paper path of the moving sheets in aprinter to provide color measurements of the test color patches printedon the sheets as they pass the color measurement device. In such coloranalysis methods, the color sensor does not contact the paper. However,color sensors may be sensitive to sensor-to-substrate distance. Hence,factors such as variations in a paper's position or differences in mediathickness may reduce color analysis accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present disclosure may be well understood, variousexamples will now be described with reference to the following drawings.

FIG. 1A schematically depicts a printing system according to examples.

FIG. 1B schematically depicts a front-view of an example of substratesupport for the printing system depicted in FIG. 1A.

FIG. 1C schematically depicts a partial perspective view of an exampleof the substrate support depicted in FIG. 1A.

FIG. 2 schematically depicts a partial top view of a substrate supportof a printing system according to examples.

FIG. 3 is a block diagram of a printing system according to examples.

FIG. 4 schematically depicts a system according to examples.

FIG. 5 is a block diagram depicting a computer readable medium accordingto examples.

FIG. 6A schematically depicts a substrate printed with color patchesaccording to examples, the substrate being supported by a substratesupport.

FIG. 6B schematically depicts a substrate printed with color patchesaccording to examples, the substrate being supported by a substratesupport.

FIG. 7 is a flow diagram illustrating examples of color analysis.

FIG. 8 schematically depicts an arrangement for determining color on asubstrate.

FIG. 9 shows a graph illustrating color measurements.

FIG. 10 shows a graph illustrating color measurements.

DETAILED DESCRIPTION

In the following, numerous details are set forth to provide anunderstanding of the examples disclosed herein. However, it will beunderstood that the examples may be practiced without these details.Further, in the following detailed description, reference is made to theaccompanying figures, in which various examples are shown by way ofillustration. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “left,” “right,” “vertical,” etc., is usedwith reference to the orientation of the figures being described.Because disclosed components can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. Like numerals are used for likeand corresponding parts of the various figures. While a limited numberof examples are illustrated, it will be understood that there arenumerous modifications and variations therefrom.

As set forth above, there are a variety of methods for analyzing colorsprinted on a substrate. However, color analysis may still beinsufficiently accurate for some specific applications. For example, inmethods in which hand-held spectrophotometers are used, since thespectrophotometer device contacts the paper, it can distort a color testpattern thereby making a color measurement inaccurate. Further, in amethod using a color sensor such as a spectrophotometer or colorimeter,since the color sensor does not contact the paper and color sensors maybe sensitive to sensor-to-substrate distance, variations in a substratevertical position may reduce accuracy of the color analysis. Suchdifferences in the vertical position between locations of a substrateare referred herein as substrate-height variability.

Further, as the present inventors have understood, some specificprinting systems may be particularly prone to substrate-heightvariability. More specifically, some printing systems may include asubstrate support for supporting the substrate, at least, in a colormeasurement zone during operation of a color sensor for color analysis.The substrate support may include projections extending from a base ofthe support and arranged to support the substrate. A projection of asubstrate support as referred herein refers to a portion raised withrespect to a support base and providing the contact surface forsupporting the substrate portion during, at least, color analysis.

The substrate support further may further include spacings to allowdeformation of the substrate towards the support base. Deformation ofthe substrate towards the support base may be desirable in order toavoid upward buckling of the substrate (upward buckling may damage thesubstrate and/or printer elements, such as a printhead, disposed aboveit). However, as can also be appreciated from FIGS. 3 and 8, substratedeformation may promote substrate-height variability. As set forthabove, substrate-height variability may render color measurementsperformed across a substrate for color analysis inconsistent.

Techniques are described herein that facilitate compensatingsubstrate-height variability influence on color analysis. In someexamples herein, substrate-height variability may be compensated byconveniently selecting how a color patch is to be printed on thesubstrate. More specifically, dimension and location in the substrate ofthe color patches may be selected such that, for each color patch, atleast a portion of the color patch can be positioned on a supportprojection in the color measurement zone when the substrate ispositioned on the substrate support for operation of a color sensor. Byway of example, the selection may be performed based on dimension andlocation of support elements such as the support projections oropenings. Thereby, dimension and location of color patches may beconveniently selected.

Further, the substrate may be positioned on the substrate support suchthat at least a portion of a color patch printed on the substrate is ona support projection. Then, color of the color patch may be determinedby operating a color sensor to acquire color of the color patch at asample portion of the color patch, the sample portion being on thesupport projection. Color calibration of the printing system may be thenbased on determined colors corresponding to sample portions being onsupport projections. Thereby, it is facilitated to reducesubstrate-height variability in the color measurements so that colorcalibration can be performed using data with better consistency.

In the following, non-limiting examples of printing systems that may beparticularly prone to substrate-height variability are illustrated withrespect to FIG. 1A-2. FIG. 1A schematically depicts a printing system100 according to examples. Printing system 100 includes a printingarrangement 102 for printing in a printing zone 103 beneath printingarrangement 102, a substrate 104 while supported by a substrate support106. A printing arrangement refers to any arrangement suitable to printa pattern (e.g., a pattern including one or more color patches) on asubstrate. An example of a printing arrangement is illustrated withrespect to FIG. 3. Examples of color patches are shown in FIGS. 6A, 6B.

A feeding mechanism 116 may be provided for advancing substrate 104towards printing zone 103, i.e., along a media advance direction 124.

A test print engine 402 may be communicatively coupled to printingarrangement 102 for causing printing of a color patch on substrate 104as described with respect to FIGS. 4-5. For performing printing, aprinthead of printing arrangement 102 may be scanned along a transitiondirection 122 (perpendicular to the plane of FIG. 1), i.e. across thewidth of substrate 104 as further illustrated with respect to FIG. 3.

In the illustrated example, printing system 100 further includes a colorsensor arrangement 110 for measuring color on substrate 104 in a colormeasurement zone 112. For performing color acquisition, color sensorarrangement 110 may be scanned along transition direction 122. A colordetermination engine 404 may be communicatively coupled to color sensorarrangement 110 for color analysis as described with respect to FIGS.4-5.

In some examples, a printing system may be configured such thatsensor-to-substrate distance with respect to a color sensor correspondsto a nominal value of the color sensor when color is acquired atsubstrate locations positioned over a support projection. Morespecifically, height of support projections may be such that, when thecolor sensor determines color of a specific substrate portion on thosesupport projections, sensor-to-substrate distance corresponds to anominal value of the color sensor.

A nominal value of a color sensor is the value, or range of values, ofsensor-to-substrate distance specified by the manufacturer to operatethe color sensor. Vertical distance between the color sensor and topportions of the substrate support may be chosen for complying with suchnominal values. (Other factors may be taken into account such as atypical substrate thicknesses or sensor angle.) A configuration of aprinting system for complying with nominal specifications of the colorsensor as described herein facilitates not only reducing measurementvariability but also improving measurement reliability.

Herein, printing systems configured as a wet ink printer are alsocontemplated. A wet ink printer is configured to use ink including arelatively high amount of water (e.g. a latex ink). A wet ink printermay include components for facilitating wet ink printing and, in view ofthe relatively high content of water of a wet ink, for promoting dryingof a printed substrate such as heating systems or pre-treatmentarrangements for fixing the ink to the substrate. In the illustratedexample, printing system 100 includes a heat source 116 for heatingsubstrate 104. In the illustrated example, heat source 116 includes aradiant source 118 (e.g., an infrared lamp). A heat source as referredto herein is intended to encompass any structure suitable to heat asubstrate in a printing zone. In examples, radiant source 118 may beconstituted by a conductive source (e.g., substrate support 106 mayintegrate a heating system for conductively heating substrate 104 suchas strip heater 207 shown in FIG. 2).

Cooling of print components of printing system 100 (e.g., a printhead inprinting arrangement 102) may be provided by a fan/blower arrangement119. For example, fan/blower arrangement 119 may generate a 2 m/sairflow over the surface of the print medium for cooling of elements inprinting arrangement 102.

Heat source 116 may be configured to heat substrate 104 to a temperatureabove 50 degrees Celsius or, more specifically, to a temperature around55 to 60 degrees Celsius. In some applications where it is desirable tocure ink ejected on substrate 104 (e.g., a latex ink), a further heatsource (not shown) may be implemented for promoting ink curing in acuring zone provided downstream printing zone 103 by heating substrate104 to a higher temperature (e.g., a temperature between 60 and 80degrees Celsius).

As an ink contacts a print medium (e.g., substrate 104), water in theink may saturate fibers of the used print medium thereby causing thefibers to expand, which in turn may cause the print medium to buckle.Buckling, also referred to as cockling, of a print medium tends to causethe print medium either to uncontrollably bend downwardly away from theprintheads, or to uncontrollably bend upwardly toward the printheads. Ineither case, a constant printhead-to-print medium spacing is notachieved, which might lead to poor print quality. Additionally, anupwardly buckling print medium may contact a printhead, which may leadto ink smearing on the print medium and/or damages in the printhead orthe print medium.

For addressing substrate buckling, a substrate support may includeopenings to allow deformation of the substrate towards a support base.In the illustrated example, substrate support 106 is constituted by aplaten including (a) ribs 120 extending from a base 126 of support 106,and (b) openings 121 (show in FIGS. 1B-1C) formed as clear spacingsbetween adjacent ribs. Ribs as referred to herein are intended toencompass any set of elongated structure suitable to support a substratewith spaces provided therebetween. Ribs may be characterized by anyshape such as a non-straight shape or, more specifically, a zigzagshape. The platen can be flat or slightly curved, depending on whichfeed arrangement is used.

In the illustrated example, conduits 138 (which can also be appreciatedin FIG. 1C) extend through base 126 to openings 121. A vacuum chamber128 may be disposed beneath base 126 for maintaining a vacuum generatedby a vacuum arrangement 130. Vacuum arrangement 130 may include a pumpsystem and/or a fan system for vacuum generation. The vacuum may befurther formed into conduits 138 and openings 121 for (a) holdingsubstrate 104 against upper surfaces of ribs 120, and (b) furtherpreventing buckling of substrate 104 towards printing arrangement 102.

Further details on substrate support 106 can be appreciated from FIGS.1B-1C. FIG. 1B schematically depicts a front-view of an example ofsubstrate support 106 for a printing system according to examples. FIG.1C schematically depicts a partial top view of substrate support 106.

Looking at FIG. 1C, ribs in substrate support 106 extend generally alongstraight paths 132 (which can be considered to be rib axes). Openings121 in the form of spacings are between adjacent ribs. Straight paths132 may be disposed along media advance direction 124 for facilitatingadvance of substrate 104 in that direction. Ribs may include a curvedshape or, more specifically, follow a zigzag path. As shown, the zigzagpath may be smooth rather than angular, e.g., following a waved profile.A zigzag path as shown in FIG. 1C reduces the length of a contactsurface between the print media and the rib in the media advancedirection, so that the contact across the substrate is distributeddiscontinuously in the media advance direction for addressing imagingartifacts that may result from support contact, as detailed in U.S. Pat.No. 7,946,700, which is incorporated herein by reference to the extentin which this document is not inconsistent with the present disclosureand in particular those parts thereof describing examples of substratesupports for printing systems.

To further reduce substrate-rib contact, ribs 120 may be formeddiscontinuously. More specifically, each of ribs 120 may include arunning straight base structure 120 a and a series of rib top portions120 b for contacting substrate 104. These rib top portions 120 b definethe highest part of substrate support 106, and act as a discontinuoussupport surface for substrate 104. Rib top portions 120 b are an exampleof projections arranged to support a substrate.

As will be understood, there are a variety of designs for substratesupports provided with openings for addressing substrate buckling. FIG.2 schematically depicts a partial top view of a substrate support 200according to examples. Support 200 includes a vacuum manifold 201, whichmay be fabricated of a thermally non-conductive material. In the exampleof FIG. 2, openings 221 are constituted as a plurality of vacuumpassageways, or ports, distributed across a projected surface 204 suchthat a vacuum can be draw down through the ports-(the vacuum beingrepresented by arrows labeled “Fv”). Further, openings 221 aredimensioned for allowing deformation of the substrate towards thesupport base.

Interspersed with the pattern of vacuum ports 203 is a set of platensurface channels 205. Inlaid within each of the channels is a stripheater 207 (other patterns and shapes may be employed). Heaters 207 areconnected to a power source (not shown) in any convenient manner. Stripheaters 207 may implement the functionality of heat source 118.

In the example of FIG. 2, projected surfaces 204 as well as strip heater207 are examples of projections arranged to support a substrate. Furtherexamples of substrate supports constituted similarly as support 200 areillustrated in U.S. Pat. No. 6,454,478, which is incorporated herein byreference to the extent in which this document is not inconsistent withthe present disclosure and in particular those parts thereof describingsubstrate supports for printing systems.

Openings, such as openings 121-221 described above, prevent substratebuckling towards a printing arrangement placed over it by allowingdeformation of the substrate towards the base of the substrate support.Moreover, such openings facilitate ink drying, which may be particularlyimportant for wet ink printing, and reduce friction between substrateand support. However, a substrate support including such spacings mayinduce substrate-height variations.

More specifically, as can be appreciated from FIGS. 3 and 8, substratebuckles 44 may be formed towards the support base at the spacings. Inthese examples, due to the platen ribs, substrate deformation isdirected towards spacings formed between the ribs. Further, in someprinting systems, the substrate is displaced along the ribs duringplacement of the substrate on the substrate support; such a displacementmay induce a wave-formed deformation along the substrate that furtherpromotes buckling forming. In general buckling formation is difficult topre-determine.

A further source for buckle formation may be vacuum generated by avacuum system (e.g., vacuum arrangement 130 in FIG. 1A) for improvingsubstrate adherence to the support. The effect of vacuum on substrateheight can be appreciated from FIG. 8: vacuum 45 generated by a vacuumsystem for improving substrate adherence to the support may stillfurther promote formation of buckles 44. By way of example, buckle size(depicted in FIG. 8 by arrow d₁) may be between 0.5 and 1 mm such as 0.7mm. Such a buckle size may be relatively significant when compared tothe sensor-to-substrate distance (depicted in FIG. 8 by arrow d₂), whichmay be between 1.2 and 3.7 mm such as 2.7 mm.

FIG. 3 further illustrates details of a print system according toexamples. FIG. 3 is a block diagram of a printing system 300 accordingto examples. Printing system 300 includes a printing arrangement 102 forprinting a pattern (not shown in FIG. 3; some examples are depicted inFIGS. 6A-6B) on substrate 104. In examples, printing arrangement 102 isconfigured for inkjet printing. Printing arrangement 102 may beconfigured to implement other printing methods such as laser printing.In the illustrated example, printing arrangement 102 includes inkprintheads 312 a-312 d for printing substrate 104 in a printing zone103. Further, printing arrangement 102 is provided mounted onto acarriage 316, which is operatively coupled to a carriage drive 318 fortraversing along transition direction 122. Carriage drive 318 may beoperatively coupled to a position registering system (e.g., acombination of a servo and an encoder) to facilitate positioning of theelements mounted on the carriage (e.g., the color sensor). Printing zone103 is a region over which printing arrangement 102 can be scanned.

In the illustrated example, carriage 316 further supports a color sensor324. Color sensor 324 is configured to provide a color output signalassociated with color of the printed pattern. The output signal of colorsensor 324 is, generally, sensitive to sensor-to-substrate distance sothat substrate-height variability may affect the result of a colormeasurement across substrate 104. As illustrated, color measurement isperformed in a color measurement zone 112, which is a region over whichcolor sensor 342 can be scanned. Since both color sensor 324 andprinting arrangement 102 are mounted on carriage 316, color measurementzone 112 and printing zone are coincident in the illustrated example.

According to some examples, a further sensor 322 (hereinafter referredto as vertical sensor 322) may be included for providing an outputsignal associated with vertical position of substrate locations.Vertical sensor 322 may be a height sensor that enables determiningsensor-to-substrate distance or a more general sensor that provides anoutput signal sensitive to sensor-to-substrate distance. Using avertical sensor facilitates compensating substrate-height variability bydynamically selecting color measurement location taking into accountsubstrate vertical position so as to reduce color measurementvariability across the sensor scan axis caused by variations in thesensor-to-substrate distance. Alternatively or in addition thereto, avertical sensor may be used for adjusting the output from color sensor324 for so as to reduce color measurement variability across the sensorscan axis caused by variations in the sensor-to-substrate distance. Suchan operation of a vertical sensor is illustrated with respect to FIG. 7.

As shown in the Figure, printing system 300 may further include asubstrate support 106 on which substrate 104, or a portion thereof, lieswhile color sensor 324 is being operated. Substrate 104 can be advancedover support 106 in media advance direction 124, which is perpendicularto the plane of the Figure. A controller 330 is configured for beingoperatively connected to the above elements of Printing system 300 aswell as an ink reservoir 332, a memory device 334, and a printjob source336.

In the illustrated example, substrate support 106 is constituted by aplaten that includes a base 126 and upstanding and spaced ribs 342. Theribs illustrated in FIGS. 2 and 6A have a straight shape along mediaadvance direction 124. As set forth above, ribs are provided forfacilitating substrate displacement as well as preventing upwardbuckling of a substrate towards a print arrangement.

As used herein, a printhead is a device including nozzle or nozzlesthrough which drops of a fluid can be ejected towards a substrate forperforming printing. The particular fluid ejection mechanism within theprinthead may take on a variety of different forms such as, but notlimited to, those using piezo-electric or thermal printhead technology.In the illustrated example, each of ink printheads 312 a-312 d isconfigured to eject ink 338 of a different color (referred to as basecolors). It will be appreciated that printing system 300 may include anynumber and configuration of printheads suitable for a particularapplication.

Ink printheads 312 a-312 d are fluidly connected to ink reservoir 332.Ink reservoir 332 includes separated reservoirs 332 a-332 d forproviding ink to the respective ink printhead. In the illustratedexample, reservoirs 332 a-332 d respectively store cyan ink, magentaink, yellow ink, and black ink. Printing systems commonly employ aplurality of ink printheads to produce secondary colors by combining inkfrom different ink printheads. Base colors are reproduced on substrate104 by depositing a drop of the required color onto a dot location.Secondary or shaded colors are reproduced by depositing drops ofdifferent base colors on adjacent dot locations; the human eyeinterprets the color mixing as the secondary color or shading.

Controller 330 is configured to execute methods described herein.Controller 330 may be implemented, for example, by one or more discreteengines and/or modules (e.g., data processing components) that are notlimited to any particular hardware, firmware, or software (i.e., machinereadable instructions) configuration. More specifically, controller 330may be configured to implement any of a test print engine 402, apositioning engine 404, a color determination engine 406, or a colorcalibration engine 408, which are illustrated below with respect to FIG.4. Controller 330 may be implemented in any computing or data processingenvironment including digital electronic circuitry, e.g., anapplication-specific integrated circuit, such as a digital signalprocessor (DSP) or in computer hardware, firmware, device driver, orsoftware (i.e., machine readable instructions). In some implementations,the functionalities of the engines and/or modules are combined into asingle data processing component. In other versions, the respectivefunctionalities of each of one or more of the engines and/or modules areperformed by a respective set of multiple data processing components.

Memory device 334 is accessible by controller 330. Memory device 334stores process instructions (e.g., machine-readable code, such ascomputer software) for implementing methods executed by controller 330,as well as data that controller 330 generates or processes to implementtechniques described herein. Memory device 334 may include one or moretangible machine-readable storage media. Memory devices suitable forembodying these instructions and data include all forms ofcomputer-readable memory, including, for example, semiconductor memorydevices, such as EPROM, EEPROM, and flash memory devices, magnetic diskssuch as internal hard disks and removable hard disks, magneto-opticaldisks, and ROM/RAM devices.

For printing a pattern on substrate 104, controller 330 may receiveprintjob commands and data from printjob source 336, which may be acomputer source or other source of printjobs. Controller 330 typicallydetermines a print mask from the received data. The print mask may bestored in memory device 334. Controller 330 is operatively connected toprinting arrangement 102 and ink reservoir 332 to control ejection ofink 338 according to the print mask. Further, controller 330 actsaccording to the print mask to provide motion control signals tocarriage drive 318 to traverse carriage 316 across substrate 104 (i.e.,in transition direction 20).

Vertical sensor 322 encompasses any type of sensor suitable to providean output signal associated with vertical position of substratelocations. A vertical position refers to a position on the substratealong an axis perpendicular to the substrate plane (i.e., a planecorresponding to a non-deformed plane). It will be understood thatsubstrate vertical position as used herein is with respect to asubstrate portion facing printing arrangement 102. Further, a substratelocation as used herein refers to a substrate portion facing printingarrangement 102. As used herein, substrate vertical position is directlycorrelated to substrate-height. Substrate vertical position may varyacross a substrate due to, for example, a varying profile of thesubstrate supports, as illustrated with respect to FIGS. 1 and 12, or avarying substrate thickness.

Each of vertical sensor 322 and color sensor 324 may be constituted by aplurality of sensors cooperating for performing the functions describedabove. Generally, vertical sensor 322 and color sensor 324 are mountedsuch that the output of vertical sensor 322 corresponds to or isindicative of sensor-to-substrate distance with respect to color sensor324. More specifically, the relative spatial configuration betweenvertical sensor 322 and color sensor 324 may be such that informationassociated with the sensor-to-substrate distance regarding color sensor324 can be inferred from the signal output of vertical sensor 322. Thisinformation may enable to (a) directly infer an absolute value of thesensor-to-substrate distance (see, e.g., the example with respect toFIG. 2), or (b) infer a parameter correlated to sensor-to-substratedistance (e.g., the vertical signal output illustrated with respect toFIG. 4). Regarding (b), in some examples the relative position betweenvertical sensor 322 and color sensor 324 is registered so thatinformation related to sensor-to-substrate distance with respect tocolor sensor 324 can be inferred from the output of vertical sensor 322.

In the example in FIG. 1, vertical sensor 322 and color sensor 324 areillustrated mounted on carriage 316. In other examples, vertical sensor322 and color sensor 324 may be mounted on another part of a printingsystem, for example, on an additional carriage capable of performingscanning over substrate 104. Vertical sensor 322 and color sensor 324may be mounted such that they can move independently from each other(e.g., by providing each sensor in independently movable carriages).

As set forth above, color sensor 324 is to provide a color output signalassociated with color of the printed pattern. A color sensor may beconstituted, for example, by a spectrophotometer or a colorimeter. Asset forth above, vertical sensor 322 is to provide an output signalassociated with vertical position of substrate locations. Verticalsensor 322 may be a distance sensor such as an ultrasound sensor or anIR sensor arranged with a pre-determined spatial configuration such thatthe signal output of the vertical sensor enables to infersensor-to-substrate distance of color sensor 324. For example, asdepicted in FIG. 1, vertical sensor 322 may be arranged in the proximityof, or adjacent to, color sensor 324 and to translate conjointlytherewith by mounting both sensors onto carriage 316. In some examples,vertical sensor 322 and color sensor 324 may be integrated within thesame sensor system as illustrated in US application with publicationnumber US2010/284009, which is incorporated herein by reference to theextent in which this document is not inconsistent with the presentdisclosure and in particular those parts thereof describing colormeasurement.

FIGS. 4-5 depict various examples of physical and logical components forimplementing various examples. In discussing FIGS. 4-5, reference ismade to FIGS. 6A-6B to provide contextual examples. Implementation,however, is not limited to these examples.

FIG. 4 depicts a system 400 for facilitating color analysis. System 400may be integrated in a printing system. For example, system 400 may beimplemented using controller 330 and memory device 334 depicted in FIG.3. In other examples, system 400 may be implemented in a computingsystem communicatively connected to a printing system for partially orcompletely performing the functionality described herein.

System 400 includes a test print engine 402 and, optionally, any of apositioning engine 404, a color determination engine 406, or a colorcalibration engine 408. Test print engine 402 is configured to causeprinting of color patches on a substrate. Some examples of color patchesprinted on a substrate 104 by operation of test print engine 402 areillustrated with respect to FIGS. 6A-6B.

FIG. 6A schematically depicts substrate 104 printed with color patches602 a-602 d, according to an example. Substrate 104 is supported bysubstrate support 606 including ribs 604. Ribs 604 constitute supportprojections arranged to support substrate 104. More specifically, ribs604 are straight and substantially flat such that the ribs supportsubstrate 104 continuously along the whole depicted rib length. In thedepicted configuration, the whole length of ribs 604 under substrate 104functions as projections arranged to support the substrate.

FIG. 6B schematically depicts a substrate 104′ printed with colorpatches 602 a′-602 c′, according to an example. (Substrate 104 and colorpatches 602 a′-602 c′ are represented transparent in FIG. 6B for thesake of illustration.) Substrate 104′ is supported by substrate support106 described above regarding FIGS. 1A-1C. Support 106 includes ribs 120with a zigzag shape. Further, ribs 120 include rib top portions 120 bthat, in the depicted configuration, function as support projectionsarranged to support substrate 104 discontinuously along the length ofribs 120.

Referring back to FIG. 4, test print engine 402 is configured to selectdimension and location in the substrate of color patches. Test printengine 402 performs this selection such that, for each of the colorpatches, at least a patch portion can be positioned on a supportprojection in the color measurement zone. By way of example, test printengine 402 may perform this selection based on dimension and location ofsupport elements such as the support projections or openings so thatdimensions and location of color patches can be conveniently selected.By way of example, selection may include dynamically computing dimensionand location in the substrate of color patches based on the spatialconfiguration of support projections. In another non-limiting example,selection may include choosing from a pre-defined set of patchdimensions and/or locations the most convenient set for a particulartype of support projections and/or openings.

Examples of the result of a selection performed by test print engine 402can be appreciated in the examples depicted in FIGS. 6A-6B. RegardingFIG. 6A, color patches 602 a-602 d are printed with dimensions andlocations on substrate 104 such that, as depicted, the color patches (inthis example, the whole area of each color patch) can be positioned oncorresponding support projections, which in this example are constitutedby ribs 604. Regarding FIG. 6B, color patches 602 a′-602 c′ are printedwith dimensions and locations on substrate 104′ such that, as depicted,a portion of each of the color patches can be positioned on acorresponding support projection, which in this example are constitutedby rib top portions 120 b. In some examples, as shown in FIG. 6A, eachof color patches 602 a-602 d can be completely positioned on acorresponding support projection. In other examples, as shown in FIG.6B, dimension and location of the color patches are selected such thatonly a portion of one or all color patches can be positioned on asupport projection.

Test print engine 402 may be further configured to select color patchdimension such that a distance between central patch portions ofadjacent color patches positioned in the color measurement zone foroperation of the color sensor corresponds to a distance between centralrib portions of adjacent ribs over which central patch portions arepositioned for operation of the color sensor. By selecting in thismanner central patch portion distances, it is facilitated that colorpatches can be conveniently positioned with respect to the supportprojections arranged to support the substrate. The result of such aselection can be appreciated in the examples in FIGS. 6A-6B.

Regarding FIG. 6A, patches 602 a-602 d are located on the substrate witha distribution corresponding to that of ribs 604. That is, the distancebetween central portions of color patches 602 a-602 d is equal tocentral portions of ribs 604 and corresponds to distance D indicated inthe Figure. In this specific example, patches 602 a-602 d, as well asthe support projections (in this example, ribs 604) are equidistantlydistributed along transition direction 122.

In other examples, e.g. as in FIG. 6B, distances between adjacentsupport projections may be not equidistant; in other words, patches maybe distributed along transition direction 122 with distances betweenadjacent patches that may differ from each other. More specifically, inthe example of FIG. 6B, since ribs 120 have a zigzag shape and are outof phase with respect to each other along media advance direction 124,distances between adjacent support projections, in this case rib topportions 120 b, varies from rib-to-rib. In this specific example, twodifferent distances D₁, D₂ between rib top portions 120 b are shown.Relative locations of color patches 602 a′-602 c′ is selectedcorresponding to the varying distances D₁, D₂.

Test print engine 402 may be further configured to select patch locationin the substrate such that the center of a first patch can be alignedover a first support projection available under the paper, when theprinted substrate is on the substrate support for color analysis. Thiscan be appreciated from the examples in FIGS. 6A-6B: in the example ofFIG. 6A, the rightmost patch (i.e., patch 602 d) can be aligned over therightmost rib 604. In the example of FIG. 6B, the rightmost patch (i.e.,patch 602 c′) can be aligned over the rightmost rib top portion 120 b.

In order to save costs associated with ink usage, it may be convenientto print a color patch with reduced dimensions. Some methods for coloranalysis require a certain patch size for averaging color measurementsover the path surface in order to compensate for substrate-heightvariability effects on color analysis. In contrast thereto, at leastsome of the examples herein do not necessarily require performing suchan averaging since substrate-height variability effects may be preventedusing a single measurement in one color patch. More specifically, atleast some of the examples herein facilitate performing color analysisusing a single measurement at a sample portion on the patch at aconveniently selected substrate height. Therefore, as the presentinventors have understood, reducing patch size in some of the examplesillustrated herein is not necessarily limited by the requirement ofperforming multiple color measurements in order to provide sufficientdata for performing an average.

Therefore, in view of the fact that a single color measurement performedon conveniently located patches may already yield a good basis for coloranalysis, test print engine 402 may be further configured to select atleast one dimension of a color patch (e.g., width or length) based on apositioning tolerance of a substrate positioning system (e.g., feedingmechanism 116 in FIG. 1A) configured to position the substrate over thesubstrate support. Note that in the other techniques referred to above,this positioning tolerance may not be the patch size constraint in viewof a minimum patch size necessary for enabling averaging color valuesfor a single patch. Taking into account substrate positioning tolerancefacilitates avoiding a misplacement of color patches relative tocorresponding projections while keeping printed patch size small.

Depending on the particularly used printing system, field of view of acolor sensor that performs color analysis of the color patch (e.g.,color sensor 324) may be the constraint for selecting reduced patchdimensions. Therefore, according to some examples, test print engine 402may be further configured to select at least one dimension of a colorpatch (e.g., width or length) based on field of view of a color sensorconfigured to perform color analysis of the color patch.

For performing the functions described above, test print engine 402 mayaccess data related to the spatial configuration of the supportprojections as well as position of the color measurement zone. This datamay be stored as part of position data 410 in data store 412.

Positioning engine 404 is configured to position a substrate printedwith color patches such that, for each color patch, at least a portionof the color patch is positioned over a support projection in the colormeasurement zone. More specifically, positioning may be performed suchthat a sample portion of a patch is over a portion of a projection in acolor measurement zone (e.g., measurement zone 112 shown in FIG. 1). Apatch sample portion refers to a portion of a patch onto which coloranalysis is to be performed.

By way of example, referring to FIG. 1, positioning engine 404 may causefeeding mechanism 116 to laterally align a substrate with supportprojections. By way of example, positioning engine 404 may operate afeeding mechanism to position the color patches in color measurementzone 112 such that a color acquisition can be performed on patchportions that are on a projection. In the example of FIG. 6A, in view ofthe straight shape of ribs 604, this can be performed directly by simplyadvancing substrate 104 along direction 124. In the example of FIG. 6A,in view of the irregular location of rib top portions 120 b, this can beperformed directly by advancing substrate 104 along direction 124 untila location is reached in which at least a portion of each color patch ison top rib portion 120 b.

Positioning engine 404 may be configured to position the substrate basedon the spatial configuration of the support projection and the colormeasurement zone. For example, positioning engine 404 may access datarelated to the spatial configuration of the printed patches and supportprojections as well as substrate position and position of the colormeasurement zone. This data may be stored as part of position data 410in data store 412. Using this data, positioning engine 404 may cause asubstrate positioning system to position the substrate such that atleast a portion of a color patch is disposed on a support projection, asdepicted in FIGS. 6A-6B.

For performing its function, positioning engine 404 may position thesubstrate based on data provided by a positioning sensor configured tomeasure substrate position using the substrate support, or anotherelement of the particularly used printing system, as reference. By wayof example, a line sensor, an example thereof is implemented inDesignjet printers (e.g., Designjet Z series) of Hewlett-Packard Company(Palo Alto, Calif., US), may be used as such a positioning sensor. Byway of example, positioning engine 404 may be configured to position thesubstrate over the substrate support such that the center of a firstpatch is aligned over a first support projection available under thepaper. In the example of FIG. 6A, the rightmost patch (i.e., patch 602d) is aligned over the rightmost rib 604. In the example of FIG. 6B, therightmost patch (i.e., patch 602 c′) is aligned over the rightmost ribtop portion 120 b.

Referring back to FIG. 4, color determination engine 406 is configuredto operate a color sensor (e.g., color sensor 110 depicted in FIG. 1A)for determining color of a color patch. More specifically, colordetermination engine 406 may cause a color sensor to generate, for eachcolor patch onto which color analysis is to be performed, a sensoroutput associated with a sample portion within the color patch. Thesample portion is over a support projection. FIGS. 6A-6B illustrate suchsample portions: regarding FIG. 6A, sample portions 603 a-603 d areassociated, respectively, with color patches 602 a-602 d; sampleportions 603 a-603 d are located within color measurement zone 112 andabove a rib portion acting as support; regarding FIG. 6B, sampleportions 603 a′-603 c′ are associated, respectively, with color patches602 a′-602 c′; sample portions 603 a′-603 c′ are located within colormeasurement zone 112 and above respective rib top portions 120 b.

From the sensor output, color determination engine 406, or any othersuitably configured computing element, may determine color of the sampleportion. Thereby, it is facilitated that color analysis is performedusing color measurements associated with substrate vertical positionscorresponding to support projections. Further, thereby, it isfacilitated consistency of color analysis with respect tosubstrate-height variability. Moreover, as set forth above, supportprojections may be arranged such that substrate locations thereon are atsensor-to-substrate distance corresponding to a nominal value specifiedfor the color sensor.

In some other examples, color acquisition engine 504 is configured todetermine color at sample portions on support projections by (i) causingand/or receiving color measurements registered with the location ofsubstrate location in which the color measurements are performed, and(ii) filtering out color measurements on the basis of location ofsubstrate location such that color measurements that correspond tosample portions on support projections are retained.

Color calibration engine 408 is to perform color calibration of aprinting arrangement. The color calibration may be based on colorsdetermined by color determination engine 404. Color calibration usingcolors acquired at sample portion over a support projection as describedherein prevents that substrate-height variability affects thecalibration results. Color calibration refers to measuring and/oradjusting color response of a printing system. Adjustment may beperformed such that color response corresponds to a known state (e.g., acolor standard). Color calibration using a selected substrate locationas described herein prevents that substrate-height variability affectsthe calibration results. It will be understood that a variety of colorcalibration methods may be used depending on the particular applicationof the color analysis. For example, color calibration may includeestablishing a known relationship to a standard color space.

The components described above with respect to FIG. 4 are implemented ascombinations of hardware and programming. Such components may beimplemented in a number of fashions. As depicted in FIG. 5, theprogramming may be processor executable instructions stored on atangible memory media 500 and the hardware may include a processor 502for executing those instructions. Memory 500 can be said to storeprogram instructions that, when executed by processor 502, implementsystem 400 of FIG. 4. Memory 500 may be integrated in the same device asprocessor 502 or it may be separate but accessible to that device andprocessor 502. In an example, memory 500 and processor 502 areimplemented in a printing system, such as printing system 300, namely,as part of memory device 334 and controller 330. In other examples,memory 500 and processor 502 are implemented in a computing systemcommunicatively coupled to a printing system for implementing thefunctionality described herein.

Examples of system 400 can be realized in any computer-readable mediafor use by or in connection with an instruction execution system such asa computer/processor based system or an ASIC (Application SpecificIntegrated Circuit) or other system that can fetch or obtain the logicfrom computer-readable media and execute the instructions containedtherein. “Computer-readable media” can be any media that can contain,store, or maintain programs and data for use by or in connection withthe instruction execution system. Computer readable media can compriseany one of many physical media such as, for example, electronic,magnetic, optical, electromagnetic, or semiconductor media. Morespecific examples of suitable computer-readable media include, but arenot limited to, a portable magnetic computer diskette such as floppydiskettes or hard drives, a random access memory (RAM), a read-onlymemory (ROM), an erasable programmable read-only memory, or a portablecompact disc.

In one example, program instructions can be part of an installationpackage that can be executed by processor 502 to implement system 400.In this case, memory 500 may be a portable medium such as a CD, DVD, orflash drive or a memory maintained by a server from which theinstallation package can be downloaded and installed. In anotherexample, the program instructions may be part of an application orapplications already installed. Here, memory 600 can include integratedmemory such as a hard drive.

In FIG. 5, the executable program instructions stored in memory 500 aredepicted as a test print module 504, a positioning module 506, a colordetermination module 508, or a color calibration module 510. Test printmodule 504, positioning module 506, color determination module 508, andcolor calibration module 510 represent program instructions that whenexecuted cause the implementation of, respectively, test print engine402, positioning engine 404, color determination engine 406, and colorcalibration engine 408 of FIG. 4.

FIG. 7 shows a flow diagram 700 that implement examples of a coloranalysis method for calibrating a printing system. In discussing FIG. 7,reference is made to the diagrams of FIGS. 1-6B to provide contextualexamples. Implementation, however, is not limited to those examples.Reference is also made to FIGS. 8-10. Again, such references are madesimply to provide contextual examples.

Referring to FIG. 7, at block 702 data associated with spatialconfiguration of elements in a printing system may be processed. Thespatial configuration data may include spatial configuration of elementsof the substrate support such as dimensions (e.g., length, width),position, and/or shape of elements of the support such as supportprojections. The spatial configuration data may further include spatialconfiguration of a color sensor configured to acquire color measurementsfor the color analysis. Referring to FIG. 4, test print engine 402 maybe responsible for implementing block 702.

Processing at block 702 may include, by way of example, receiving thedata from an external system, accessing stored data (e.g., spatialconfiguration data stored as part of position data 410 in data store412, or receiving a user input. In examples, spatial configuration datamay be previously acquired by a printed system using suitably configuredsensors (e.g., a distance sensor operated over an unloaded substratesupport). Processing at block 702 may also include transforming thespatial configuration data (e.g., changing units, or absolute spatialreferences) so that the data can be used to determine the pattern to beprinted.

At block 703, dimension and location in a substrate of color patches maybe selected such that, for each color patch, at least a portion of thecolor patch can be positioned on a support projection in the colormeasurement zone when the substrate is positioned on the substratesupport for operation of a color sensor. Data processed at block 702 maybe used to implement block 703. For example, position and location ofsupport projections may be inferred at block 702; from this information,the dimension and location of color patches can be computed that enableto position the substrate over the substrate support such that, for eachcolor patch, at least a portion of the color patch can be positioned ona support projection in the color measurement zone. This computation maybe performed iteratively. For example, position and location of a firstpatch may be computed using as reference a first support projection(e.g., a support rib); then position and location of a second patch maybe computed using as reference a further support projection adjacent tothe first support projection; these steps may be repeated until positionand location of all patches to be printed are computed. Referring toFIG. 4, test print engine 402 may be responsible for implementing block703.

At block 704, a test pattern may be printed on a substrate includingcolor patches with dimension and location selected at block 703. Someexamples of test patterns that may result from block 704 are illustratedwith respect to FIGS. 6A-6B. Referring to FIG. 4, test print engine 402may be responsible for implementing block 704.

At block 706, a substrate with a test pattern printed at block 704 maybe positioned on a substrate support. The substrate support includes i)projections extending from a base of the support, the projectionsarranged to support the substrate, and ii) openings to allow deformationof the substrate towards the support base. Some examples of suchsubstrate support are illustrated above with respect to FIGS. 1A-2. In amore specific example, block 706 may include positioning at least aportion of a color patch over a support projection taking into account,at least, dimension and location of the color patch. As set forth above,the test pattern may be printed by taking into account the spatialconfiguration of the substrate support such that patch portions can bepositioned on support projections. The positioning is performed suchthat, for each color patch, a sample portion of the color patch is overa portion of a projection in a color measurement zone. Some examples oftest patterns positioned over a substrate support according to block 706are illustrated with respect to FIGS. 6A-6B. Referring to FIG. 4,positioning engine 404 may be responsible for implementing block 706.

At block 708, color of color patches may be determined. For example,color may be determined at sample portions in a color measurement zoneof the printing system, the sample portion being over the supportprojection. Some examples of sample portions are illustrated withrespect to FIGS. 6A, 6B (see sample portions 603 a-603 d or 603 a′-603c′). Further examples of sample portions at which color measurements maybe performed are illustrated in FIG. 8 by arrows 846.

Block 708 may include causing a color sensor to acquire color of a colorpatch at a sample portion that is located over a support projection.Referring to FIG. 4, color determination engine 406 may be responsiblefor implementing block 708.

According to some examples, the color sensor may be translated over thesubstrate while acquiring color only at the sample portions. Forexample, as illustrated by FIG. 8, color sensor 24 may be operated toacquire color only at selected locations 846 while being scanned along atransition direction 122. In other examples, the color sensor may betranslated over the substrate while acquiring color only at thelocations that do not necessarily overlay with support projections; acolor determination may then include filtering a set of colormeasurement for processing color measurements associated with the sampleportions that are over support projections.

There are a variety of methods for determining the specific spatiallocation of sample portions, i.e. the absolute positions at which colormeasurements are to be acquired. By way of example, this specificspatial location may be determined by taking into account the spatialconfiguration of the substrate support, location of the colormeasurement zone, and location of the color patches. For example, aprinting system may register substrate location and, from thatinformation, infer positions of patch portion; using absolutereferences, patch portions overlapping support projection and colormeasurement zone may then inferred after the substrate is positioned. Anencoding system coupled to color sensor may be then used to position thecolor sensor for color acquisition at the sample portions.

In other examples, the specific spatial location of sample portions maybe determined dynamically. For example, block 708 may include selectinga color measurement location (i.e., a sample portion as used herein)based on a distance measurement indicative of sensor-to-substratedistance of the color sensor. The selection is performed such that acolor measurement location coincides with a support projection.

Such a distance measurement may be performed by a further sensor (e.g.,vertical sensor 322) configured for providing an output signalassociated with vertical position of substrate locations. Such a furthersensor may be, for example, a distance sensor (i.e., a sensor with whicha specific substrate vertical position can be determined) or a sensorthat is sensitive to sensor-to-substrate distance such as adensitometer. The sample locations may be determined by analyzing, forexample, a substrate-height profile, or a profile of a signal outputcorrelated to substrate-height to infer the spatial location of supportprojections.

Determining color of a printed pattern at a sample portion over thesupport projections facilitates improving color measurement quality (inparticular measurement reliability) as compared to conventional methods,as illustrated by FIGS. 9-10. Both Figures are graphs showing ESP CIE-L*measurements across different substrates lying on a substrate supportconstituted by a ribbed platen: curves 902 a-902 b correspond to anOffset substrate; curves 904 a-904 b correspond to a Vynil substrate(Avery MPI 3000). FIG. 9 shows color curves 902 a-904 a acquired withoutconsidering whether sample portions are over support projections. Incontrast thereto, FIG. 10 show color curves 902 b-904 b acquired usingsample portion over support projections. As can be appreciated, colorcurves shown in FIG. 10 are characterized by a lower variability ascompared with the color curves in FIG. 9. By way of example, usingsample portion over support projections may facilitate an accurate colormeasurement with variability below 2 CIEDelta E1976 (or Euclideandistance in CIELabspace). This may translate into a 4× reduction ofmeasurement variability across printer platen as compared to othermethods.

According to some examples, block 708 may include adjusting colormeasurements using measurements associated with substrate verticalposition of the selected sample locations for compensatingsubstrate-height variability. Color measurement adjustment facilitates afurther compensation of substrate-height variability, which may stillinfluence color analysis even when color measurements are performed atsample portions located over support projections.

Generally, color adjustment is performed using a previouscharacterization of how color measurements depend on substrate-height. Avariety of methods may be used for adjustment of the color measurement.For example, an adjustment matrix may be stored that correlates thefollowing parameters: (a) adjustment factors; and (b)sensor-to-substrate distances; a determined substrate-height may beassociated with a corresponding sensor-to-substrate distance; thesensor-to-substrate distance may be used to identify an adjustmentfactor using the adjustment matrix; finally, a color measurementcorresponding to the sensor-to-substrate distance may be adjusted byapplying the adjustment factor.

Some examples of methods for adjusting color measurements based onsensor-to-substrate distances are illustrated in US application withpublication number US 2011/0032526, which is incorporated herein byreference to the extent in which this document is not inconsistent withthe present disclosure and in particular those parts thereof describingcolor measurement adjustment.

At block 710, color calibration of the printing system used for printingthe test pattern at block 704 may be performed based on color determinedat block. Referring to FIG. 4, color determination engine 406 may beresponsible for implementing block 708. For performing colorcalibration, color measurements at sample portions corresponding todifferent color patches may be used. For example, one color measurementper color patch may be used. Using the color determination, the printersystem used to print the pattern may be color calibrated as illustratedabove with respect to FIG. 4.

Color calibration as described facilitates reducing color patch size ascompared with some other methods in which substrate-height variabilityof color measurements is compensated by (i) measuring color at multiplelocations within one color patch (e.g., 4 samples per patch), and (ii)averaging the multiple color measurements for the color patch.Acquisition at multiple locations generally implies a higher patch area.In contrast thereto, examples herein facilitate reducingsubstrate-height variability of color measurements using a singlemeasurement per patch. Further, these other methods may require Npatches for a specific substrate width W so that multiple measurementsper patch and a useful average can be obtained; in contrast thereto, atleast some examples herein may be performed such that 2N patches fit thesame specific width W. Hence, substrate area (and length) required by atleast some examples herein may require 35% of the substrate arearequired by at least some other methods.

As a further advantage, in at least some examples herein, the amount ofink and paper spent in printing a test color pattern can be reducedsince patch size can be kept relatively small. Moreover, thereby theamount of time can be reduced since the time used to print and measure atest color pattern for color calibration can be kept relatively low. Byway of example, a calibration target of 64 color patches may take 40seconds using substrate selection compared to 2 min 25 sec of some othermethods. As a further remark, at least some examples herein facilitatesperforming color calibration using color measurements at the nominalsensor-to-substrate distance specified for the color sensor. In contrastthereto, some other methods do not ensure that color calibration isperformed at the nominal sensor-to-substrate distance specified for thecolor sensor, thereby, compromising calibration reliability.

In the foregoing description, numerous details are set forth to providean understanding of the examples disclosed herein. However, it will beunderstood that the examples may be practiced without these details. Forexample, it will be understood that a substrate support as used hereinis not limited to a ribbed platen. Further, it will be understood thatexamples herein are not limited to wet ink printers. While a limitednumber of examples have been disclosed, numerous modifications andvariations therefrom are contemplated. It is intended that the appendedclaims cover such modifications and variations. Claims reciting “a” or“an” with respect to a particular element contemplate incorporation ofone or more such elements, neither requiring nor excluding two or moresuch elements. Further, the terms “include” and “comprise” are used asopen-ended transitions.

What is claimed is:
 1. A printing system for printing a substrate, theprinting system comprising: a color measurement zone in which a colorsensor is to determine color of color patches printed on the substrate;a substrate support for supporting the substrate at least in the colormeasurement zone during operation of the color sensor, the substratesupport including projections extending from a base of the substratesupport and arranged to support the substrate, and openings to allowdeformation of the substrate towards the base; and a test print engineto cause printing of a given color patch of the color patches on thesubstrate, the test print engine to select a location of the given colorpatch printed onto the substrate, the selecting of the location causingpositioning of at least a portion of the given color patch printed onthe substrate to be over a given projection of the projections of thesubstrate support; and a color determination engine to operate the colorsensor to determine color of the given color patch while at least theportion of the given color patch is over the given projection.
 2. Theprinting system of claim 1, wherein the projections are part of ribsextending from the base, and the openings correspond to spacingsprovided between adjacent ribs.
 3. The printing system of claim 2,wherein the test print engine is to select the location of the givencolor patch such that a distance between central patch portions ofadjacent color patches positioned in the color measurement zonecorresponds to a distance between central rib portions of adjacent ribsover which the central patch portions are positioned for operation ofthe color sensor.
 4. The printing system of claim 1, wherein the testprint engine is to select at least one dimension of the given colorpatch based on a positioning tolerance of a substrate positioning systemconfigured to position the substrate over the substrate support.
 5. Theprinting system of claim 1, further comprising a substrate positioningsystem to position the substrate such that, for each respective colorpatch of the color patches, at least a portion of the respective colorpatch is positioned over a respective projection in the colormeasurement zone.
 6. The printing system of claim 5, wherein thesubstrate positioning system is to position the substrate based on aspatial configuration of the respective projection and the colormeasurement zone.
 7. The printing system of claim 1, wherein theprinting system includes a printing arrangement for wet ink printing. 8.A non-transitory tangible computer readable storage medium comprisinginstructions that, when executed by a processor, cause a printing systemto: select a location of a color patch printed onto a substrate on asubstrate support including projections and openings between theprojections, the selecting of the location causing positioning of atleast a portion of the color patch printed on the substrate to be over agiven projection of the projections of the substrate support, theopenings to allow deformation of the substrate towards a support base ofthe substrate support; and cause a color sensor to acquire color of thecolor patch at a sample portion of the color patch, while the sampleportion is over the given projection.
 9. The medium of claim 8, furthercomprising instructions to cause the printing system to print the colorpatch on the substrate with a patch dimension and a patch location inthe substrate selected based on a dimension and a location of thesupport projection.
 10. The medium of claim 8, further comprisinginstructions to perform color calibration of the printing system basedon determined colors of sample portions being over the projections. 11.A method comprising: printing a test color patch on a substrate;selecting a location of the test color patch printed onto the substrateon a substrate support including: projections extending from a base ofthe substrate support, the projections arranged to support thesubstrate, and openings between the projections to allow deformation ofthe substrate towards the base, the selecting of the location causingpositioning of at least a portion of the test color patch to be over agiven projection of the projections of the support substrate when thetest color patch is in a color measurement zone; and determining colorof at least the portion of the test color patch while at least theportion of the test color patch is in the color measurement zone.
 12. Amethod comprising: printing a test pattern on a substrate, the testpattern including a plurality of color patches; positioning thesubstrate printed with the test pattern on a substrate supportincluding: projections extending from a base of the support, theprojections arranged to support the substrate, and openings to allowdeformation of the substrate towards the support base, the positioningbeing performed such that, for each color patch, a sample portion of thecolor patch is over a portion of a projection in a color measurementzone; and determining color of the color patches at the sample portionsin the color measurement zone, wherein the projections are part of ribsextending on the base, the openings correspond to spacings providedbetween pairs of adjacent ribs, and the color patches are printed suchthat a distance between central portions of adjacent color patchescorresponds to a distance between central portions of adjacent ribs. 13.The method of claim 12, wherein printing the test pattern includesprinting the color patches with distances between the central patchportions of adjacent color patches equal to distances between thecentral portions of adjacent ribs in the color measurement zone.